Conventional strapping machines feed a strip of strapping material around an article forming an overlapped portion of the strap, after which the strap is tensioned and the overlapped portions are fastened together and a feed portion is severed from the loop fastened about the article. The overlapped portions may be fastened by methods involving either (i) crimping a separate sealing member onto the overlapped portions or (ii) die-cut notching the overlapped portions of the strap. This latter method is commonly known as the seal-less method because a separate sealing member is not used.
An example of an automatic seal-less head type of strapping machine is shown in U.S. Pat. No. 3,804,001. This head utilizes a cutter blade and cooperating anvil to sever the strap after the overlapped portions are notched and fastened together by the dies. The dies are actuated in sequence by a rotary cam shaft, the last die actuated carrying the cutter blade for severing the strap. This mechanism assures that the overlapping strap is fastened before the feed portion is severed from the loop. However, the mechanism required is complicated and includes many bearings, cams and other parts to accomplish this function. A simpler mechanism for actuation of the dies is shown in U.S. Pat. No. 3,794,086. A hydraulic cylinder actuates all the dies and the shear blade simultaneously. A problem with this design can arise from premature severing of the strap if there is a space between the feed portion of the strap and the underlying strap portion at the location of the shear blade. This space results from the close position of the feed rollers with respect to the seal-less head which necessities feeding the strap through an entry guide aligned at an inclined angle with respect to the seal-less head. An example of such a configuration is shown in U.S. Pat. No. 3,804,001. Of course, it is desirable to have the feed mechanism positioned close to the head to provide a compact machine. To eliminate an angularly aligned entry guide would require remote positioning of the feed rollers so that a horizontal entry could be obtained at the location of the head. Another problem is that no provision is made for shearing different thicknesses of strap. The shears are set for severing a narrow range of strap thicknesses upon assembly of the machine and cannot be adjusted for severing other strap thicknesses without shutdown and disassembly of the machine.
It is known to provide for tilting of the head to remove the dies from the strap after the overlapped portions are fastened together. This arrangement has the advantage of permitting the dies to be housed together as a unit in the head as distinguished from the split die arrangement shown in U.S. Pat. No. 3,794,086. The unitary arrangement, in turn, helps main proper die alignment which is critical for obtaining a securely fastened joint in the overlapped strap. However, prior designs have been rather complicated because of the tilting mechanisms. For example, the whole head and die-actuating mechanism is tilted in the design shown in U.S. Pat. No. 3,545,499. U.S. Pat. No. 3,804,001 shows tilting of the head and feed mechanism, although not the motor for actuating the dies. Another disadvantage of the prior designs is that a separately actuated tilting mechanism was required.
Finally, prior seal-less head designs contain provision for adjusting the spacing of the dies over only a narrow range. Such heads are not able to handle as wide a range of strap thicknesses as desired. Furthermore, the adjustment was made on a trial-and-error basis, requiring independent measurement of the die spacing after each adjustment.